1. Field of the Invention
The present invention relates to a dielectric film which comprises tantalum oxide (Ta.sub.2 O.sub.5) as a major component, and which is applicable to a dielectric film for an electroluminescent (hereinafter abbreviated to "EL") display device, an electrochromic (hereinafter abbreviated to "EC") display device, a large-scale integrated (hereinafter abbreviated to "LSI") circuit, or the like.
2. Description of the Related Art
As the LSI circuit technologies and the display device technologies have been developing, there has been arising need, ever increasing day by day, for a dielectric film material which has a high dielectric constant as well as a high insulation property. For instance, silicon dioxide (SiO.sub.2) has been used extensively in most of the dielectric films for the capacitors which are used in the field of the LSI circuits conventionally. However, as ICs have become highly integrated, electronics engineers have longed for a material which has a higher dielectric constant than SiO.sub.2 does and which has a higher insulation property so as to ensure a higher reliability. Likewise, there has been such need also in the fields of the EL display devices, the EC display devices, and so on.
However, no materials have been available so far which have high dielectric constants and at the same which maintain high insulation properties. Accordingly, in order to satisfy this requirement, there was proposed a stacked construction in which different types of dielectric films were stacked. Despite the proposal, the stacked construction resulted in complicated manufacturing processes. Consequently, SiO.sub.2 is used in most (99% or more) of the LSI circuits, EL display devices, the EC display devices, or the like at present.
In addition, tantalum oxide (Ta.sub.2 O.sub.5) has a dielectric constant which is 7 to 8 times that of SiO.sub.2, and accordingly there was a tryout in which Ta.sub.2 O.sub.5 was used independently. However, this Ta.sub.2 O.sub.5 film exhibited a large leakage current. The greater the amount of current leakage, the smaller the insulation property becomes. As a result, the Ta.sub.2 O.sub.5 film suffered from the problem that it should be formed in a large thickness. Hence, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 45,008/1985, Japanese Unexamined Patent Publication (Kokai) No. 57,959/1985 and Japanese Unexamined Patent Publication (Kokai) No. 17,177/1987, a couple of methods have been proposed in which aluminum (Al), SiO.sub.2, titanium dioxide (TiO.sub.2), silicon nitride (Si.sub.3 N.sub.4), or the like is added to or stacked on the Ta.sub.2 O.sub.5 film. However, no particular advantages are gained by these films. Further, the manufacturing processes required to form the films are complicated, especially the manufacture of stacked films.